Broadband wireless is expected to be one of the main drivers of the telecommunications industry. There is a substantial increase in demand for broadband connectivity, with personal broadband being the key growth engine for mobile wireless broadband networks.
Communication in such networks is generally divided between access and backhaul. An access network is the air interface network providing traffic communication between mobile terminals (subscribers) and their associated access points (base stations), while a backhaul network is the air interface network providing traffic communication between the various base stations and a core network. The networks may be arranged to transfer data alone, as in Wi-Fi networks, or may be arranged for triple play services (video, audio and data), typically WiMax (or other competitive technology, such as 3GPP-LTE). In conventional systems, the access network and the backhaul network each require their own separate transmission equipment, antennas, etc, at great cost to the operator.
One example of a conventional backhaul network is connecting wireless base stations to corresponding core mobile networks (ASN GateWay, AAA servers, etc). The choice of backhaul technology must take into account such parameters as capacity, cost and coverage. Base station backhaul typically is performed via wired infrastructure (e.g., E1/T1 leased lines), or via wireless Point-to-point (PTP) microwave links to each base station, which is expensive to deploy (equipment and installation). In particular, due to the direct, uninterrupted line-of-sight requirements of the wireless backhaul equipment, the backhaul components of conventional base stations require strategic deployment location on high and expensive towers.
Mobile WiMAX, as defined in IEEE Standard 802.16e-2005 Standardization for WiMAX, was originally designed to provide mobile broadband access for mobile devices, i.e., broadband wireless data-optimized technology, providing carrier-grade triple play services using a variety of user devices (such as laptops, PDAs, handheld devices, smart phones, etc.). A complete mobile WiMAX Radio Access Network (RAN) requires deployment of massive infrastructure, including base station sites with high towers, base station equipment, antennas, and a separate backhaul network, as described above.
There are also known outdoor Wi-Fi networks, deployed mainly according to outdoor Wi-Fi mesh technology. The typical Wi-Fi setup contains one or more Access Points (APs), which is the equivalent terminology to Base Station in WiMax, having relatively limited range, deployed along telephone poles, street poles, electricity poles and rooftops. Due to the access point unit's smaller coverage range, a large number of access point units are required to cover a given area. Conventional outdoor Wi-Fi access point units require costly power amplifiers in each Wi-Fi AP unit to extend the coverage range. In addition, conventional Wi-Fi networks operate only on unlicensed bands and suffer from severe interference and difficult radio-planning issues.
Furthermore, in the micro/pico-cell deployment approach of conventional Wi-Fi-mesh networks, due to multiple access point nodes in the network, backhauling becomes more complicated and costly. Backhauling each node via wired lines (E1/T1 or DSL) is impractical in a dense deployment of nodes. On the other hand, backhauling each node via traditional wireless PTP microwave links is expensive due to costly equipment and installation costs and not feasible to deploy on telephone poles, street poles, electricity poles, etc. In Wi-Fi, like in WiMAX, PTP microwave links require high towers to achieve a clear line-of-sight between nodes. In addition, when the network load is increased, the backhaul network losses drastically degrade the overall network performance (capacity and latency).
In multi-hop and mesh deployments, there can be a problem of interference in backhaul transmissions between adjacent links during concurrent transmission over the same frequency band in a cluster of nodes. In this network, it is difficult to determine what is channel noise and what is interference from adjacent links, and there is no way to determine how much of the interference is caused by which link. In order to determine the interference, at present, a node must perform channel sounding. This involves stimulating the transmitter to send a signal and measuring the signal received (amplitude and phase) on each antenna. Since the channel is known, the interference can be calculated. It will be appreciated by those skilled in the art that at present, it is only possible to measure the overall results of interference on a link or node, e.g., SINR or CINR. However, these measurements do not indicate the source of the interference or the relative contributions of several interfering links near the link of interest.
Consequently, there is a long felt need for a method for interference measurement including channel estimation to permit interference mitigation in an in-band backhaul network. The resulting backhaul link would be characterized by robust point-to-point (PTP) communication conditions, in the sense of Signal to Interference and Noise Ratio (SINR) and potential throughput.